1. Field of the Invention
This invention relates to a two piece cranial bolt having a threaded portion to engage the skull and a lumen portion to engage the threaded portion.
2. Discussion of the Related Art
For certain medical conditions, such as head trauma, it is necessary to place sensors into the brain of the patient. Many of the prior art devices are designed to penetrate the skull, and be fixed in place to allow for the passage of a sensor probe or catheter to the brain. However, most prior art bolts have one opening that allows for only one probe or catheter to reach the brain through the skull. The prior art devices do not allow for multiple readings at the same location or do not allow for a reading or multiple readings to be taken along with the placement of a catheter to drain pressure building up inside the cranium. These prior art devices require the drilling of multiple holes in a patient's skull or the necessary probes and catheters must be removed and replaced as readings or drainage is required.
U.S. Pat. No. 3,055,370 to McKinney et al. (“McKinney”) discloses a tap assembly 10 including a tap 11 and holder 12. A single tubular member 13 extends through both tap 11 and holder 12 to allow needle 34 to pass through. Tubular member 13 can change orientation because it passes through ball 14, located inside tap 11 and under holder 12. Holder 12 is threaded into tap 11 and applies force to ball 14 to lock tubular member 13 at the correct orientation. However, McKinney only allows for one instrument at a time to pass through tubular member 13 and it cannot be converted to allow for multiple passageways because of the design of the locking mechanism using holder 12, i.e. only one passageway can be accommodated per tap assembly because of ball 14. McKinney suggests that tap 11 and holder 12 can be assembled once tap 11 is threaded into the patient's skull. However, undue stress will be applied to the patient's skull if tap assembly 10 is assembled after tap 11 is seated in the skull. A particular amount of force is required to assure that ball 14, and thus tubular holder 13, does not move once needle 34 is in place. This force causes undue stress on the patient's skull. U.S. Pat. No. 4,903,707 to Kunte et al. (“Kunte”) has similar problems to McKinney wherein bolt means 17 is screwed into the patient's skull 15 and catheter 19 is held in place by clamping means 21 which must be screwed down on bolt means 17.
Another example is U.S. Pat. No. 6,356,792 to Errico et al. (“Errico”) which discloses a skull mounted electrode lead securing assembly. Cylindrical skull port member 100 is fitted into a burr hole in the patient's skull. Lead locking element 120 is fitted to the inner surface of port member 100 and allows a single electrical lead to pass through an axial channel 126. However, the crucial element of Errico's invention is lead locking element 130, 132. Sliding element 132 is designed to partially occlude axial channel 126 to prevent the movement of the lead. Errico's invention is not suited for multiple passageways because the locking mechanism requires too much space on the surface of the lead locking element to allow for other passageways on the same lead locking element. Additionally, one skilled in the art would not insert multiple electrodes in Errico's lead locking element because these electrodes would be too close to each other, thereby resulting in inaccurate measurements.
An example of a cranial bolt having multiple channels is illustrated in Great Britain Patent No. 2,300,080 to Hutchinson. Hutchinson discloses a single bolt 2 containing a plurality of channels 4 through which instruments may pass to reach the brain. However, Hutchinson's channels 4 converge toward the centerline c of bolt 2 and any instruments passed through these channels will intersect each other a very short distance from inner end 12. The intersection of the multiple instruments poses a problem because every probe that is introduced into the brain tissue causes a certain amount of trauma. Thus, another probe or catheter placed next to a first probe will disturb the readings of the first probe. The first probe will record readings stemming from the trauma and not the actual readings of the patient's brain.
Thus, there is a need in the art for a two piece multiple passageway cranial bolt where each of the implements passed toward the brain diverge in directions toward different areas of the brain to allow for accurate readings of the patient's brain.